Enhanced Capabilities for Formation Testing Tools with a Highly Sophisticated Pump Control System

摘要

Formation testing tools in wireline operations typically use hydraulic pump systems for fluid cleanup and sampling. As there is an electric connection and a communications channel suitable for interactive tool operation to the wireline systems, the operator interacts continuously with the system and can adjust the pump parameters to the downhole conditions. Due to the low bandwidth of the mud pulse systems this is not possible in the while-drilling environment. Moreover, the hydraulic concept makes a precise control of the pump parameters nearly impossible. To overcome this challenge a highly sophisticated pump and pump control system is necessary. A closed-loop control system and different intelligent algorithms avoid pumping below the bubblepoint and thus prevent the alteration of the fluid sample. In combination with pressure gauges the innovative pump control system delivers additional information about the downhole fluid. While pumping it is possible to calculate continuously the compressibility of the fluid and deliver a precise cleanup mobility. The pump control minimizes the backflow and mud valve switching force and it is possible to derive the effective volume pumped that corrects the difference between pump rate and flow rate. In this paper the capabilities and operation of this innovative pump system within the new logging-while-drilling (LWD) fluid analysis and sampling tool will be shown. It will be demonstrated that it is possible to run a fluid sampling operation in a nearly automated system. The continuous interaction of the operator with the system to control the pump process will not be necessary. The results from different field tests will be compared and the advantages of the system will be discussed. An outlook will be given how to implement this technology in further developments and how sampling tools can benefit from this technology in challenging environments like unconsolidated sands.